A comparison of Hα and stellar scale lengths in Virgo and field spirals

The scale lengths of the old stars and ionized gas distributions are compared for similar samples of Virgo Cluster members and field spiral galaxies via Hα and broad R-band surface photometry. While the R-band and Hα scale lengths are, on average, comparable for the combined sample, we find significant differences between the field and cluster samples. While the Hα scale lengths of the field galaxies are a factor of 1.14 ± 0.07 longer, on average, than their R-band scale lengths, the Hα scale lengths of Virgo Cluster members are, on average, 20% smaller than their R-band scale lengths. Furthermore, in Virgo, the scale length ratios are correlated with the size of the star-forming disk: galaxies with smaller overall Hα extents also show steeper radial falloff of star formation activity. At the same time, we find no strong trends in scale length ratio as a function of other galaxy properties, including galaxy luminosity, inclination, morphological type, central R-band light concentration, or bar type. Our results for Hα emission are similar to other results for dust emission, suggesting that Hα and dust have similar distributions. The environmental dependence of the Hα scale length places additional constraints on the evolutionary process(es) that cause gas depletion and a suppression of the star formation rate in clusters of galaxies.